Field of the Invention
The invention relates to a quantum well structure and a method for manufacturing the same, and more particularly, to a multiple quantum well structure and a method for manufacturing the same.
Description of Related Art
When material dimensions are reduced to nanometer scale, not only the dimensions are considerably miniaturized, but also some quantum effects such as confinement effects, surface and interface effects, and tunneling effects become particularly apparent. These characteristics may be applied to electronic component development, biochip fabrication, sensitivity enhancement of medical instruments, and so on.
More specifically, due to particle and wave nature of electrons, in a nanomaterial, a length of an electron wave function is close to a feature size of a quantum structure, and the wave nature of electrons is sufficiently shown. Therefore, when a material is reduced to nanometer scale in a direction, the quantum confinement effect will appear in the direction. At this moment, the electrons are confined to move freely in a two-dimensional space constituted by the other two dimensions, and such system is called a quantum well. The quantum well utilizes a semiconductor layer having a larger band gap as a barrier layer and a semiconductor layer having a smaller band gap as a well layer. In the quantum well, which is a well-like band structure formed by the well layer clamped by the barrier layers from two sides, carriers are easily confined, thus enhancing light emission efficiency.
During fabrication of the quantum well, a heterostructure is usually grown, for example, gallium nitride (GaN) and indium gallium nitride (InGaN) multiple quantum well structures are grown. When lattices of two grown heterostructure materials do not match each other, stress will accumulate in the structure. As growing thickness increases, the accumulated stress increases. When the stress exceeds a threshold value, the material layers cannot bear the stress anymore and the stress has to be released in other ways. Accordingly, epitaxial defects are usually caused, leading to damage to the multiple quantum well structure, and further decreasing the light emission efficiency.